Fluorescent brighteners are a class of fluorescent materials that absorb light in the ultraviolet regions of the electromagnetic spectrum (e.g., less than 400 nm) and re-emit light in the violet and blue regions of the electromagnetic spectrum (e.g., greater than 400 nm). Fluorescent brighteners have been used in a variety of applications, e.g., in a laundry detergent composition, to enhance the color or appearance of materials, such as treated fabrics. Generally, fluorescent brighteners are used to increase the perceived whiteness of such materials by increasing the overall amount of blue light emanating from the material, i.e., reflected from the material and emitted by substances deposited on the material.
Fluorescent brighteners are typically in a particulate form and therefore added into liquid compositions via liquid premixes. Forming a fluorescent brightener premix and adding the premix to the liquid composition, rather than adding particulate fluorescent brighteners directly to the liquid composition, allows for more evenly distribution of the fluorescent brightener in the liquid composition. Also, good physical stability (i.e., a stable viscosity profile and no phase splitting) is desired for fluorescent brightener premixes as this property enables a prolonged storage of the premix prior to being added into liquid compositions.
In traditional fluorescent brightener premixes, monoethanolamine (MEA) is the main solvent used to dissolve particulate fluorescent brighteners, e.g., brightener 15 (disodium 4,4′-bis {[4-anilino-6-morpholino-s-triazin-2-yl]-amino}-2,2′-stilbenedisulfonate). MEA is known to act as a counterion to fluorescent brighteners and thus provides improved physical stability to the premix. However, MEA is a primary amine characterized by partial protonation in an aqueous solution and capable of receiving a hydrogen ion from water, resulting in an increase of the OH-ion concentration in the solution (i.e., higher pH of the solution). Thus, upon being added into a liquid composition, such fluorescent brightener premixes containing MEA impact the pH of the liquid composition significantly. This significant pH change of the liquid composition in the manufacturing process is undesired as it requires further pH adjustment equipments or steps. In an in-line process, the issue becomes even more severe due to the precise control of each added ingredient required by an in-line process.
Thus, there is a need for a fluorescent brightener premix that, upon being added into a liquid composition, has minimized impact on the pH of the liquid composition. In particular, the present invention provides a fluorescent brightener premix that has a relatively neutral pH when diluted, compared with those premixes in the art.
It is an advantage of the present invention to provide a fluorescent brightener premix that is physically stable during storage.
It is another advantage of the present invention to provide a physically stable fluorescent brightener premix that does not require either agitation or heating during storage.
It is yet another advantage of the present invention to provide a physically stable fluorescent brightener premix from a variety of fluorescent brightener raw materials, including those containing impurities.
It is even yet another advantage of the present invention to provide an in-line process of making a liquid cleaning composition comprising a fluorescent brightener mix, without requiring a further pH adjustment equipment or step.